1. Field of the Invention
The present invention generally relates to spinal fixation systems for correction of spinal deformities or injuries, and embodiments of the invention relate to an instrument for moving a vertebra or vertebrae to a desired position.
2. Description of Related Art
Spinal disorders, degenerative conditions, or trauma may result in a need to correct or stabilize the spine of a patient. A variety of spinal fixation systems may be used to correct and/or stabilize a spine. A spinal fixation system may be classified as an anterior, lateral, or posterior system according to a position of the system relative to the spine. Anterior and lateral spinal fixation systems usually include short structures that support only a few adjacent vertebral bodies of a spine. Several anterior and lateral spinal fixation systems may be coupled to vertebral bodies to correct and/or stabilize a large portion of the spine. Posterior stabilization systems often include pairs of vertically aligned rods for stabilizing both short and long segments of a spine.
A posterior spinal fixation system may include a pair of bendable rods that are contoured and longitudinally disposed adjacent to vertebral bodies of a spine. Rods used in a fixation system are typically circular in cross section, although rods having non-circular cross sections may also be used. The rods may be attached to vertebral bodies of the spine by a plurality of fixation elements. The fixation elements may be hooks and/or bone screws. Transverse connectors may be used to join the pair of spinal rods together. Transverse connectors may stabilize and provide rigidity to a spinal fixation system.
A fixation element may include a connector that attaches the fixation element to a spinal rod. One type of connector includes an opening that snaps onto a spinal rod. When a spinal rod is positioned in the opening of a connector, a fastener, such as a bolt or a locking plate, may securely attach the connector to the fixation element. The fastener may inhibit motion of the spinal rod relative to the fixation element. U.S. Pat. No. 6,132,430 issued to Wagner, which is incorporated by reference as if fully set forth herein, describes fixation elements wherein fixation element connectors are configured to snap onto spinal rods. Other types of fixation elements may also be used in a spinal fixation system. Fixation elements may include, but are not limited to, the fixation elements shown and described in U.S. Pat. Nos. 4,763,644; 4,805,602; 4,887,596; 4,950,269; 5,129,388; 5,961,518; 5,989,250; 5,997,539; and 6,063,089; each of these patents being incorporated by reference as if fully set forth herein.
A spinal rod may be attached to one or more vertebrae during a posterior spinal fixation procedure. A vertebra or vertebrae that are not in desired positions may be moved during a spinal fixation procedure. A fixation element may be attached to a vertebra that needs to be moved. A translation instrument may be used to draw the fixation element and the spinal rod together. A fastener may then be attached to the fixation element to join the rod and the element together.
A translation device that may be used to join a fixation element and a spinal rod together is the Universal Spinal System Rod Introduction Pliers from Synthes Spine (Paoli, Pa.). One of the jaws of the pliers has a hollow barrel. The other jaw is a rod contactor. The pliers are used with a holder that threadably attaches to a fixation element. After attaching the holder to the fixation element, the holder is inserted into the hollow barrel. Grips of the pliers are squeezed together by a user to cause the rod contactor to rotate and contact a spinal rod. Continued squeezing of the grips forces the rod and the fixation element together so that the rod may be positioned within an opening of the fixation element. A user of the translation device must adjust the position of the holder within the barrel to ensure that the rod is positioned within the fixation element when the grips of the translation device are closed together. Proper alignment of the translation device may be difficult to achieve during use of the translation instrument. A user may have to manually adjust the vertical position of the fixation element while simultaneously translating the fixation element and the rod together.
U.S. Pat. No. 5,020,519 to Hayes et al., which is incorporated by reference as if fully set forth herein, describes a device that may be used to introduce a rod into an opening in a spinal implant. The system includes a one-piece tool that clamps a spinal implant and aligns a rod with an opening in the spinal implant. The device may be used to reduce the vertical offset between the rod and the implant. The spinal implant must be maintained in the correct position in the translation device while threading the rod into place between the jaws.
A translation instrument may be used to move a vertebra or vertebrae to a desired position. A spinal rod may be attached to vertebral bodies by fixation elements. An adjacent fixation element may be attached to an out-of-position vertebra. It may be desirable to move the spinal rod and the adjacent fixation element together so that the vertebra is placed in a desired position relative to adjacent vertebrae. Securing the fixation element to the spinal rod may allow for proper alignment of vertebral bodies of a spinal column.
A translation instrument may be used to move the spinal rod and the adjacent fixation element together. The translation instrument may simultaneously translate the fixation element towards the rod and adjust the vertical height of the fixation element relative to the rod so that the rod is positioned within a rod opening of the fixation element. A guide of the translation instrument may engage the fixation element or an extension member coupled to the fixation element. The guide may ensure that the spinal rod is properly positioned relative to a fixation element when the translation instrument is used.
A fixation element may be coupled to a vertebral body whose position is to be adjusted. A fixation element may be, but is not limited to, a bone screw or a hook. A holder may be coupled to the fixation element. The holder may include an attachment mechanism, a shaft, and a guide. The attachment mechanism may securely attach the holder to the fixation element. The shaft may allow the holder to be coupled to a positioner of a translation instrument. The holder guide may be a protrusion that extends from a side of the shaft.
A translation instrument may include a positioner, an arm, and an actuator. A positioner may couple a fixation element holder to the translation instrument. In an embodiment, the positioner may allow the holder to move axially relative to the translation instrument.
An arm of a translation instrument may be pivotally coupled to an actuator of the translation instrument. The actuator may be a pair of lever arms or grips that are pivotally coupled together. When the grips are grasped and moved towards each other, the arm may move towards a holder placed within a positioner of the translation instrument. The arm may include a guide configured to mate with a guide of the holder. The arm may also include a rod engager. In an embodiment, the rod engager may be an indentation or groove in a body of the arm that contacts and holds a rod. The arm guide contacts the holder guide during use to adjust a position of the translation instrument relative to a fixation element. Grasping and moving the grips towards each other may rotate the arm so that the rod engager contacts a rod. Moving the grips closer together may bring the rod and the fixation element together. The holder guide may interact with the arm guide as the grips are moved towards each other. Contact of the holder guide with the arm guide may adjust a position of the translation instrument relative to the fixation element so that the rod and a rod opening of the fixation element may be brought together. After the rod is placed within the rod opening, the fixation element may be attached to the rod.
A guide of a fixation element holder and a guide of a translation instrument may interact to allow a rod held by the arm to be positioned in a rod opening of a fixation element. Using the holder guide and the translation instrument guide to adjust a position of the translation instrument relative to the fixation element may eliminate the need to manually guide a rod to a rod opening while simultaneously translating a vertebra or vertebrae to an adjusted position.
A translation instrument may include bias or spring members that influence a separation distance between grips of the instrument. The bias members may force the grips apart when a user does not apply a compressive force to the grips. When the grips are positioned fully apart from each other, the translation instrument is in an initial position. When the translation instrument is in the initial position, an arm of the translation instrument is in a position rotated away from a holder that is coupled to a positioner of the translation instrument. As the grips are moved together, the arm rotates towards the holder. If a user releases the grips, the biasing members may return the grips to the initial position.
A translation instrument may include a position retainer that resists forces applied to the grips by the bias members. In an embodiment, the position retainer may include a serrated member that is pivotally coupled to a first grip. The serrations may be configured to engage a portion of a second grip. The engaging portion of the second grip may be an end of the grip. The serrations are oriented to allow the grips to be moved towards each other, but resist movement of the grips away from each other. During use, a user may rotate the serrated member so that the member contacts the engaging portion of the second grip. The user may then move the first grip towards the second grip to rotate an arm towards a holder that is coupled to a positioner of the translation instrument. The user may stop the movement of the grips towards each other. If the user stops movement of the grips towards each other, the position retainer may allow the position of the arm to remain fixed relative to the holder. If the user desires to rotate the arm towards an initial position, the user may rotate the serrated member away from the engaging portion. Force applied to the grips may be removed to allow the bias members to return the grips, and the arm, towards the initial position.
In an embodiment, a position retainer of a translation instrument may be located at an end of the translation instrument. The location of the position retainer at the end of the translation instrument may allow a user convenient access to the position retainer during use with a hand that is not grasping the instrument. The location may also allow convenient access to the position retainer by a member of a surgical team who is not grasping the translation instrument.
A position retainer may also include a locking mechanism. The locking mechanism may be used to fix a position of a serrated member so that grips of the translation instrument are fixed relative to each other. Fixing the position of the grips relative to each other may inhibit accidental release of the position retainer. In an embodiment, the locking mechanism may be a hook that is pivotally attached to a second grip near an engaging portion of the second grip. When the hook is rotated so that the hook contacts the serrated member, movement of the grips towards or away from each other may be inhibited. When the hook is rotated away from the serrated member, the grips may be moved towards each other, or the serrated member may be rotated away from the engaging portion so that the grips may be moved away from each other.
An advantage of using a translation instrument to position a vertebra or vertebrae is that the translation instrument may simultaneously translate and vertically adjust the position of the vertebra or vertebrae. A position of a rod opening of a fixation element that may be coupled to an out-of-position vertebra may be adjusted relative to a position of a rod when the translation instrument is used. The translation instrument may ensure that the rod is placed within the rod opening during use. The fixation element may then be coupled to the rod. The translation instrument may eliminate the need to manually adjust a vertical position of the rod opening relative to the rod while simultaneously adjusting the lateral position of the rod opening relative to the rod.
A further advantage of a translation instrument may be that the translation instrument includes bias members that return the translation instrument to an initial position when grips of the instrument are released. The bias members may eliminate the need to manually close the grips and manually open the grips during use.
Another advantage of a translation instrument may be that the translation instrument includes a retention mechanism that inhibits grips of the translation instrument from returning to an initial position during use. The translation instrument may also advantageously include a locking member that fixes the position of the grips relative to each other and prevents accidental release or adjustment of the translation instrument.
Further advantages of a translation instrument may be that the translation instrument is sturdy, durable, lightweight, safe, simple, efficient, reliable and inexpensive; yet the translation instrument may also be easy to manufacture and use.